Constraining Z‑Matrix Bond Lengths or Angles in Jaguar Input

To freeze bond lengths or angles during a geometry optimization, add a # sign after the coordinate values. For example, to fix the HOH bond angle of water to be 106.0°, you could enter the following Z‑matrix:

O
H1  O   0.9428
H1  O   0.9428   H1   106.0#

In a geometry optimization on this input geometry, the bond angle remains frozen at 106° throughout the optimization, although the bond lengths would vary. For more details, see Constraining Coordinates in Jaguar Calculations, which describes how to set up constraints for optimizations.

To constrain two geometric parameters to be the same during a geometry optimization, use variables in Z‑matrix input (see Variables and Dummy Atoms in Jaguar Z‑Matrix Input). To freeze variables during an optimization, add a # sign to the end of the variable setting in the variable definition section. In this example, the C–H bond is frozen at 1.09 Å:

chbond=1.09#  HCHang=109.47

You can also freeze the average of a set of all possible dihedral angles about a given bond. This average is called a “natural torsional coordinate” [103]. To set up a natural torsional coordinate, you specify the bond in a coord section and mark it with #nt, as in the example below. Jaguar automatically determines all of the torsional angles about this bond, averages them, and constrains the averaged coordinate to its initial value in an optimization.

&coord
C1 C2 #nt
&